The present invention is directed generally to an improved method for determining the steering ratio of a vehicle.
To an increasing extent, electronic systems for improving vehicle safety, such as, for example, anti brake-lock systems (ABS), electronic stability programs (e.g., ESP: electronic stability program; ESC: electronic stability control) or programs for preventing vehicle rollover (RSC: roll stability control), are being built into modern vehicles. To ensure that these electronic systems operate as efficiently and safely as possible, numerous different vehicle parameters and sensor measurements are sensed and evaluated.
In this respect, the steering angle of the vehicle has proved to be an important parameter. In some electronic systems (such as in ESP and ESC or in RSC), a control action such as active engagement of the vehicle brakes is exerted as a function of steering angle. Exact sensing of the steering angle is therefore very important for such a control action.
The measure conventionally used for the steering angle is the rotation of the vehicle's steering wheel (steering wheel angle), which is sensed by means of a steering wheel angle sensor mounted on the steering column of the vehicle. The steering angle of the vehicle, that is, the angular displacement of the steered vehicle wheels, is then inferred from the angular displacement of the steering wheel. In this approach, either a constant value is assumed for the steering ratio over the entire steering range, or, in other words, for the ratio between the rotation of the steering wheel and the rotation of the steered vehicle wheels, or several values are used for the steering ratio as a function of different steering wheel angles, in order to represent as realistically as possible nonlinear steering ratios caused by the existing steering geometry. Conventionally, these values had to be laboriously determined and manually input into, for example, an electronic stability program (e.g., ESP, ESC).
Accordingly, it is desired to provide a method for determining the steering ratio of the vehicle in a simple and cost-effective manner.